Various types of truck trailers (e.g., semi-truck trailers) are commonly equipped with sliding tandem systems. A sliding tandem system provides a means for repositioning the rear axle(s) of a trailer to thereby redistribute the load weight being carried by the trailer axles.
As depicted in FIGS. 1-4, a sliding tandem system 2 will typically include: (a) a pair of fixed suspension rails 4 provided on the underframe of the trailer, each of said fixed rails 4 having a series of positioning holes or slots 6 provided therein; (b) a sliding suspension frame 8 slidably mounted on fixed suspension rails 4; and (c) a suspension locking assembly 10. A typical suspension locking assembly 10 will include: a plurality of (typically four) locking pins 12 which are selectively positionable in fixed rail positioning holes 6; springs or other biasing means 14 associated with locking pins 12 for biasing pins 12 toward their locked positions (i.e., toward engagement with fixed rail positioning holes 6); an elongate rotatable shaft 16 which extends parallel to fixed suspension rails 4; linkage assemblies 18 which operably associate locking pins 12 with elongate shaft 16 such that, by rotating shaft 16 about its longitudinal axis, locking pins 12 can be selectively extended or retracted; a crank arm 20 having the top end thereof connected to the end of elongate shaft 16; and a hand operated pin-pulling rod/member 22. Pin-pulling rod 22 is connected to the bottom end of crank arm 20 such that (a) by pulling rod 22, elongate shaft 16 is rotated to withdraw locking pins 12 from their locked positions and (b) by releasing rod 22, elongate shaft 16 is allowed to rotate in the opposite direction such that as a result of the force exerted by springs 14, locking pins 12 move into locking engagement with positioning holes 6.
A sliding tandem system 2 of the type depicted in FIGS. 1-4 will also typically include means for retaining locking pins 12 in their unlocked positions so that sliding suspension frame 8 can be repositioned on fixed suspension rails 4. Such retaining means will typically comprise notches 24 formed on pin-pulling rod 22. Notches 24 mate with the narrow portion of a keyhole slot 28 provided in the side of sliding suspension frame 8. At the same time that rod 22 is pulled to unlock pins 12, notched portion 24 of rod 22 can be secured in the narrow portion of keyhole slot 28 to thereby retain rod 22 in its pulled position.
Sliding tandem systems are disclosed, for example, in U.S. Pat. Nos. 2,900,194, 3,778,079, 4,838,566, and 4,838,578. The entire disclosure of each of these patents is incorporated herein by reference.
Unfortunately, when locking pins 12 are received in fixed rail positioning holes 6, the edges of positioning holes 6 tend to bind against locking pins 12 so that pins 12 cannot readily be removed therefrom. Consequently, a sliding tandem system of the type depicted in FIGS. 1-4 typically cannot be unlocked without the efforts of two people, one of whom is seated in the truck cab and the other of whom is positioned adjacent the rear axle(s) of the trailer. The person positioned in the truck cab rocks the trailer back and forth in order to free (i.e., unbind) the locking pins. At the same time, the person positioned adjacent the rear axle(s) continuously pulls pin-pulling rod 22 such that, at the brief instant when the locking pins are freed, pins 12 are pulled to their unlocked position.
As will thus be apparent, a need has existed for a pin pulling system which will allow one person, acting alone, to quickly and easily unlock a sliding suspension system. Oftentimes, particularly when on the road, a second person is not available to assist in the pin-pulling operation. Without the assistance of a second person, hours of effort may be required to unlock a sliding suspension system.
As will also be apparent, a need has existed for a pin pulling system which eliminates the need to have a person gripping the pin pulling rod while the trailer is rocked back and forth. The person gripping pin-pulling rod 22 during the unlocking operation is placed in great danger of being seriously injured by the trailer tires, the pin-pulling rod and/or the trailer body.
U.S. Pat. No. 4,838,566 discloses a modified sliding tandem system which can be unlocked without requiring that a second person operate the pin-pulling rod while the trailer is rocked back and forth. In one embodiment, the modified sliding tandem system of U.S. Pat. No. 4,838,566 is composed of: an extended, rotatable suspension shaft; a plate rigidly secured to the shaft at a location spaced apart from the end of the shaft; a crank arm rigidly attached to a spacer and received over the end of the suspension shaft such that the crank arm and spacer are able to rotate about the end portion of the shaft; a coil spring which encircles the spacer and has a first end secured to the plate and a second end secured to the crank arm; and a pin-pulling rod secured to the lower end of the crank arm. The pin-pulling rod is operable for pivoting the crank arm to thereby withdraw the suspension system locking pins. When the locking pins are stuck in extended position, the coil spring will deflect so that the pin-pulling rod can be pulled and secured in its pulled position. With the rod thus secured, the coil spring operates to urge the suspension shaft to rotate such that the locking pins will retract as soon as the binding forces holding the pins in locked position are released.
A second embodiment of the modified suspension system of U.S. Pat. No. 4,838,566 is composed of: an extended suspension shaft having a hollow end portion; a torsion bar-type spring secured in the hollow end portion of the shaft; a crank arm connected to the end of the torsion bar spring and rotably positioned on the end of the shaft; and a pin-pulling rod operably connected to the crank arm. If one or more of the locking pins is stuck, the bar spring will twist on its axis so that the rod can be pulled and the crank arm can be rotated independently of the shaft. The pin-pulling rod can then be secured in pull position whereby the bar spring will impart a continuous force to the shaft which urges the locking pins to retract as soon as the binding forces holding the pins in extended position are released.
Although the modified suspension systems of U.S. Pat. No. 4,838,566 represent clear improvements in the art, the U.S. Pat. No. 4,838,566 systems have various shortcomings. For example, the U.S. Pat. No. 4,838,566 suspension systems do not provide a mechanism which can be easily attached to, and used for unlocking, an existing sliding suspension system. Moreover, the conversion of an existing sliding suspension system to include features of the type disclosed in U.S. Pat. No. 4,838,566 would require numerous system modifications. Further, none of the assemblies disclosed in U.S. Pat. No. 4,838,566 provides an operational backup system which can be used in the event that the shaftrotating spring mechanism fails.
U.S. Pat. No. 4,838,578 also discloses a modified suspension system which can be unlocked without requiring that a second person operate a pin-pulling rod while the trailer is rocked back and forth. The system of U.S. Pat. No. 4,838,578 includes: an elongate cylindrical housing having a sidewall which is attached to the bottom end of an unlocking system crank arm; a pin-pulling rod received through an end of the cylindrical housing; and a coiled compression spring which encircles the pulling rod and is contained within the cylindrical housing. If one or more locking pins are stuck in extended position, the compression spring will deflect such that the pulling rod can be pulled and secured in its pulled position. With the rod thus secured in pulled position, the spring urges the cylindrical housing to move outwardly to recapture the pulling rod. The eventual outward movement of the cylindrical housing operates to pivot the crank arm whereby the suspension system is unlocked.
Compared to the systems of U.S. Pat. No. 4,838,566, the system of U.S. Pat. No. 4,838,578 can more readily be used to modify an existing sliding suspension assembly; however, the U.S. Pat. No. 4,838,578 system also has significant shortcomings. As is apparent from the drawings provided in U.S. Pat. No. 4,838,566 and in U.S. Pat. No. 4,838,578, the U.S. Pat. No. 4,838,578 system is not as sturdy and as reliably constructed as the U.S. Pat. No. 4,838,566 systems. Further, the U.S. Pat. No. 4,838,578 system does not provide an operational backup assembly which can be used in the event that the cylinder and spring assembly fails.